Local anesthetic block of sympathetic nerves during heavy rhythmic exercise increased forearm blood flow from 35.4 to 50.7 ml/100 ml/min and O2 uptake from 45.5 to 54.2 ml/kg/min (P<0.05).
Does sympathetic modulation affect blood flow and oxygen uptake in active muscles during rhythmic exercise in humans?
Sympathetic nerves modulate blood flow to active muscles during exercise, and this restraint can limit oxygen uptake during heavy rhythmic exercise.
Absolute Event Rate: 50.7% vs 35.4%
p-value: p=< 0.05
This study tested the effects of sympathetically mediated changes in blood flow to active muscles on muscle O2 uptake (VO2) in humans. Four minutes of graded (15-80% of maximum voluntary contraction, MVC) rhythmic handgrip exercise were performed. Forearm blood flow (FBF) (plethysmography) and deep vein O2 saturation were measured each minute. Forearm O2 uptake was calculated using the Fick principle. In protocol 1, exercise was performed while supine and again while upright to augment sympathetic outflow to the active muscles. Standing reduced FBF at rest from 3.6 to 2.2 ml.100 ml-1.min-1 (P < 0.05). During light exercise (15-40% MVC) FBF was unaffected by body position. Standing reduced FBF (P < 0.05) from 36.0 to 25.2 ml.100 ml-1.min-1 and forearm VO2 from 38.2 to 28.1 ml.kg-1.min-1 during the final work load. In protocol 2, exercise was performed while supine before and after local anesthetic block of the sympathetic nerves to the forearm. Sympathetic block increased FBF at rest from 3.1 to 8.9 ml.100 ml-1.min-1 (P < 0.05), and FBF was higher during all work loads At 70-80% of MVC sympathetic block increased FBF from 35.4 to 50.7 ml.100 ml-1.min-1 (P < 0.05), and forearm VO2 from 45.5 to 54.2 ml.kg-1.min-1 (P < 0.05). These results suggest that in humans sympathetic nerves modulate blood flow to active muscles during light and heavy rhythmic exercise and that this restraint of flow can limit O2 uptake in muscles performing heavy rhythmic exercise.
Joyner et al. (Thu,) reported a other. Local anesthetic block of sympathetic nerves vs. Before sympathetic block was evaluated on Forearm blood flow at 70-80% of maximum voluntary contraction (ml/100 ml/min) (p=< 0.05). Local anesthetic block of sympathetic nerves during heavy rhythmic exercise increased forearm blood flow from 35.4 to 50.7 ml/100 ml/min and O2 uptake from 45.5 to 54.2 ml/kg/min (P<0.05).